Several Republican presidential candidates said they’d go to war with Iran to prevent it from acquiring nuclear weapons, days after the International Atomic Energy Agency warned that the Middle Eastern nation could be pushing in that direction.

But the general sense of agreement over policies pretty much ended there during Saturday’s debate on foreign policy, with the candidates spelling out sharp differences on water-boarding, drone strikes against U.S. citizens and foreign assistance to Pakistan.

Mitt Romney sounded the alarm early about the implications the next presidential election will have on Iran’s developing the capacity to build a nuclear weapon.

“If we re-elect Barack Obama then Iran will have a nuclear weapon,” the former Massachusetts governor said.

To prevent the Middle Eastern nation from moving in that direction, several of the candidates agreed that the federal government must combine stiffer economic sanctions, support for the nation’s dissidents and operations aimed at eliminating the scientists and systems involved.

“First of all, maximum covert operations to block and disrupt the Iranian program, including taking out their scientists, including breaking up their systems, all of it covertly, all of it deniable,” Mr. Gingrich said.

But they did not all agree on whether - or when - to use military force.

Former Pennsylvania Sen. Rick Santorum argued that the United States and Israel should be planning military strikes against Iran’s nuclear development sites. Herman Cain said that he “would not use military means at this time,” while Mr. Romney and Mr. Gingrich said they’d resort to military force as a last resort.

Texas Rep. Ron Paul pushed in a different direction on this issue, arguing that “it is not worth war to prevent the Iranian nuke” and even if he did think it was a good idea, Congress would have to authorize military action through a declaration of war.

The topic of Iran kicked off the questions in the 90-minute debate at Wofford College, where the candidates, including Texas Gov. Rick Perry, Rep. Michele Bachmann, and former Gov. Jon Huntsman, juggled questions over funding for Pakistan, the president’s plan to wind down the wars in Iraq and Afghanistan and the emergence of China.

“Some say the 21st Century is the century of China, but I don’t believe that,” Mr. Perry said. “Reagan said that Russia will end up on the ash heap of history. I think the Communist Chinese government will end up on the ash heap, too.”

With less than two months to go before the Iowa caucuses kick off the nomination process and roughly a year out from the presidential election, South Carolina Republicans plan to play a major role in the process, noting that they’ve been a bellwether in GOP nomination battles, correctly tapping the eventual nominee in every race since 1980.

“We will pick the winner,” South Carolina GOP Chairman Chad Connelly predicted before the debate.

The national security and foreign policy focus of the debate proved timely, coming on the heels of a new report from the United Nations’ nuclear watchdog that said Iran was conducting experiments “relevant to the development of a nuclear device.”

It also came as Italian Premier Silvio Berlusconi stepped aside because of the nation’s financial mess, and the Arab League’s vote to suspend Syria and push toward sanctions if the government of President Bashar al-Assad does not end the crackdown on anti-government protestors.

Story Continues →“It is time for the Assad dictatorship to end and we should use covert activity to do that,” Mr. Romney said.

Mrs. Bachmann warned at one point, that “we need to understand the intricacies of the Middle East. Iran is working through proxies like Syra,” she said. “The table is being set for worldwide nuclear war against Israel.”

Mr. Paul also had a bone to pick with President Obama’s decision to green light the drone attack that killed Anwar al-Awlaki, the American born al-Qaida operative without a trial.

Mr. Romney and Mr. Gingrich took a harder line however, with the former House speaker saying, “if you engage in war against the United States you are an enemy combatant. You should not go to court.”

Mr. Paul, Mr. Huntsman, Mr. Romney, Mr. Gingrich, Mr. Cain, and Mrs. Bachmann all also took issue with whether the United States should use water-boarding.

“We have a name brand in the world,” said Mr. Huntsman. “I have lived overseas four times and been an ambassador three times. We project liberty, democracy and human rights. Water-boarding is torture. If we lose the ability to project values, then we lose it all.”

The debate comes with polls showing a change in the leading contenders.

Mr. Cain is still running strong, though a shadow has been cast over his campaign after news stories unearthed allegations of sexually inappropriate behavior in the 1990’s while he led the National Restaurant Association. Mr. Cain has maintained the charges were unsubstantiated and his campaign has said that the news stories have created a backlash that translated into an uptick in fund raising.

Mr. Perry, meanwhile, is in the midst of damage control from an embarrassing moment in Wednesday’s debate where he couldn’t recall the third of three federal agencies he wanted to cut. Eventually, he remembered it was the Department of Energy, which is responsible for handling the nation’s nuclear weapons and nuclear reactors.

The events have opened the door for Mr. Gingrich to try to present himself as the more conservative alternative to Mr. Romney, who thanks to name identification and his proven fund-raising prowess, is seen as the man to beat.

A realclearpolitics.com average of polls on Saturday showed Mr. Romney with a thin lead over Mr. Cain in the polls. The latest CBS poll, though, put Mr. Gingrich tied for second with the former Masschusetts governor.